In endoscopic retrograde cholangiopancreatography (ERCP), a radiopaque dye is introduced through an endoscope (a flexible viewing tube), which is inserted into the mouth and through the stomach into the duodenum (the first segment of the small intestine). The radiopaque dye is injected into the biliary tract just past the sphincter of Oddi. The dye then flows back up the biliary tract and often shows the pancreatic ducts.

Surgical instruments can also be used with the endoscope, allowing a doctor to remove a stone in a bile duct or insert a tube (stent) to bypass a bile duct blocked by scarring or cancer.